U.S. patent number 5,247,026 [Application Number 07/901,349] was granted by the patent office on 1993-09-21 for randomly epoxidized small star polymers.
This patent grant is currently assigned to Shell Oil Company. Invention is credited to Steven H. Dillman, James R. Erickson, Dale L. Handlin, Jr., Robert J. Sutherland, Carl L. Willis.
United States Patent |
5,247,026 |
Erickson , et al. |
September 21, 1993 |
Randomly epoxidized small star polymers
Abstract
An epoxidized diene star polymer having greater than 4 arms and
comprising from 0.05 to 5 Meq of di-, tri- and tetra-substituted
olefinic epoxides and the molecular weights of the arms are from
1,500 to 15,000.
Inventors: |
Erickson; James R. (Katy,
TX), Dillman; Steven H. (Houston, TX), Handlin, Jr.; Dale
L. (Houston, TX), Willis; Carl L. (Houston, TX),
Sutherland; Robert J. (Houston, TX) |
Assignee: |
Shell Oil Company (Houston,
TX)
|
Family
ID: |
25413998 |
Appl.
No.: |
07/901,349 |
Filed: |
June 19, 1992 |
Current U.S.
Class: |
525/331.9;
525/314; 525/333.3; 525/901 |
Current CPC
Class: |
C08C
19/06 (20130101); C08C 19/44 (20130101); Y10S
525/901 (20130101) |
Current International
Class: |
C08C
19/00 (20060101); C08C 19/06 (20060101); C08C
19/44 (20060101); C08F 236/10 () |
Field of
Search: |
;525/901,331.9,333.3,314 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0295026 |
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Dec 1988 |
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EP |
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0438287 |
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EP |
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0449374 |
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Oct 1991 |
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EP |
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3442200 |
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May 1986 |
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DE |
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219779 |
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Mar 1985 |
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DD |
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249029 |
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Aug 1987 |
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DD |
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256709 |
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May 1988 |
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DD |
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61-042504 |
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Mar 1986 |
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JP |
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61-136563 |
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Jun 1986 |
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JP |
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62-257904 |
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Nov 1987 |
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JP |
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1-115978 |
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May 1989 |
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JP |
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1035928 |
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May 1963 |
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GB |
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1294890 |
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Nov 1972 |
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GB |
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Other References
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19, pp. 607-623, published in 1982. .
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Crosslinking of Hot Melt PSA's", by J. R. Erickson Pub. May 1985.
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Carbocationic Polymerization by Joseph P. Kennedy, pp. 82 and
138-140, published in 1982. .
"Radiation Curing of PSA's Based on Thermoplastic Rubbers", by D.
J. Clair, Mar. 1980 Adhesives Age. .
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Polymers", by D. N. Shulz, S. R. Turner and M. A. Golub, Rubber
Chemistry and Technology 5, 1982, pp. 809-959. .
"Epoxidation of Polybutadiene and Styrene-Butadiene Triblock
Copolymers with Monoperoxyphthalic Acid: Kinetic and Conformation
Study", by W. Huang, G. Hsiue and W. Hou, Journal of Polymer
Science: Part A: Polymer. .
"Transition-Metal-Catalyzed Epoxidations", by K. A. Jorgensen,
Chemical Reviews, vol. 89, No. 3, May 1989, pp. 431-457. .
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published in 1978 by Technology Marketing Corporation, pp. 23-77.
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in 1982 by John Wiley & Sons, pp. 41-136. .
"Cationic Polymerization: Iodonium and Sulfonium Salt
Photoinitiators", by J. V. Crivello, Advances in Polymer Science
62, 1985, pp. 1-48. .
"UV Curing of Epoxides by Cationic Polymerization", by William R.
Watt, Radiation Curing, Nov. 1986, pp. 7-25. .
"Light Sources", by Vincent D. McGinnis of Battelle Columbus
Laboratories. .
"New Transparent Flexible UV-Cured Films from
Polyisobutylene-Polyisoprene Block Polymers", Journal of
Macromolecular Sci.-Chemistry, by Puskas, Kaszas and Kennedy, vol.
A28, No. 1, 1991. .
Research Disclosure 311115, Star Branched Polymers From Linear
Polymer Terminated by Epoxy Moieties, Disclosed
Anonymously..
|
Primary Examiner: Bleutge; John C.
Assistant Examiner: Aylward; D.
Attorney, Agent or Firm: Haas; Donald F.
Claims
We claim:
1. An epoxidized diene star polymer having a random distribution of
from 0.1 to 3 Meq of di-, tri- and tetrasubstituted olefinic
epoxides per gram of polymer and greater than 4 arms wherein the
arm molecular weight is from 1500 to 15,000.
2. The polymer of claim 1 wherein the arms are primarily
1,4-polyisoprene.
3. The polymer of claim 1 wherein the arms are primarily
1,4-polybutadiene.
4. The polymer of claim 1 wherein the polymer is hydrogenated such
that less than 1 Meq of olefinic double bonds per gram of polymer
remain in the polymer.
5. The polymer of claim 1 wherein the polymer is crosslinked
through at least some of the epoxy functionality by exposure to
radiation.
6. The polymer of claim 1 wherein the polymer is chemically
crosslinked through at least some of the epoxy functionality.
7. An adhesive composition comprising the polymer of claim 1.
8. An adhesive composition comprising the polymer of claim 5.
9. An adhesive composition comprising the polymer of claim 6.
10. An epoxidized conjugated diolefin star polymer of the
formula
wherein D is (A--M.sub.p); and
wherein A is a block comprising at least one diene and the
molecular weight of A 1s from 1,500 to 15,000; and
wherein the polymer contains a random distribution of from 0.1 to 3
Meq of di-, tri- and tetra-substituted olefinic epoxides per gram
of polymer; and
wherein C is a block or multiblock segment which has a molecular
weight of 50 to 15,000 and comprises at least one diene or vinyl
aromatic hydrocarbon or methacrylate or combinations thereof but is
not identical to D; and
wherein the A blocks may comprise up to 99% of a monoalkenyl
aromatic hydrocarbon monomer; and
wherein M is a miniblock of a monomer selected from the group
consisting of vinyl aromatic hydrocarbons and dienes and has a
molecular weight of 50 to 1000; and
wherein X is a coupling agent or coupling monomers or initiator,
n.gtoreq.2, r.gtoreq.0, n.gtoreq.r, n+r ranges from greater than 4
to 100 and p is 0 or 1.
11. The polymer of claim 10 wherein A is primarily 1,4
polyisoprene.
12. The polymer of claim 10 wherein A is primarily
1,4-polybutadiene.
13. The polymer of claim 10 wherein the polymer is hydrogenated
such that less than 1 Meq of olefinic double bonds per gram of
polymer remain in the copolymer.
14. The polymer of claim 10 wherein the polymer is crosslinked
through at least some of the epoxy functionality by exposure to
radiation.
15. The polymer of claim 10 wherein the polymer is chemically
crosslinked through at least some of the epoxy functionality.
16. An adhesive composition comprising the polymer of claim 10.
17. An adhesive composition comprising the polymer of claim 14.
18. An adhesive composition comprising the polymer of claim 15.
19. The polymer of claim 1 wherein the polymer contains 0.2 to 1
Meq/g of olefinic epoxides.
20. The polymer of claim 10 wherein the polymer contains 0.2 to 1
Meq/g of olefinic epoxides.
Description
BACKGROUND OF THE INVENTION
This invention relates to diene based, epoxidized star polymers
suitable for crosslinking and adhesive, sealant and coating
compositions made therefrom.
High molecular weight diene based styrenic block copolymers such as
the family of KRATON.RTM. S-I-S, S-B-S, S-EP-S and S-EB-S block
copolymers are extensively used as base polymers in the formulation
of many types of hot melt applied coatings and adhesives. These
materials offer advantages over other types of materials such as
acrylic oligomer/acrylic monomer and polyol/isocyanate monomer
systems that are applied as 100% reactive systems and are cured by
chemical or radiation means. An important advantage of the high
molecular weight diene based styrenic block copolymers is the
ability to provide non-polluting formulations and method of
application that employs very benign raw materials, compared to the
substantial risk associated with acrylate and isocyanate monomer
based 100% reactive systems.
However, an important limitation of the styrenic block copolymers
has been the inability to provide formulations with solvent and
higher temperature resistance. This is because the styrenic block
copolymers rely on physical association of the polystyrene blocks
in the polymer for crosslinking and once the polystyrene domains in
the polymer are weakened by solvent takeup or temperatures near or
above the glass transition temperature of the polystyrene, cohesive
strength is lost. This problem has been solved by the preparation
of very high molecular weight block copolymers such as KRATON.RTM.
D1320X rubber which can undergo covalent crosslinking by EB
radiation to reinforce the physical crosslinking to give improved
solvent and heat resistance. Another important limitation of the
styrenic block copolymers is related to the otherwise very
desirable hot melt application method. Many substrates cannot
tolerate being exposed to hot melt temperatures, 300.degree. F. to
450.degree. F., without being severely damaged. This is the case
for very thin polyolefin films, such as thin polyethylene film.
The present invention provides relatively high molecular weight
diene based polymers having a very compact star structure with
short arms which lowers the viscosity. These polymers do not have a
distinct styrene block which would tend to raise application
viscosity. The polymers of this invention have many of the property
advantages of conventional styrenic block copolymers, including
being safe to handle and being covalently crosslinkable for solvent
and high temperature resistance. Additionally, the polymers of this
invention can be applied as warm melts or as a 100% reactive so
that they can be used on heat sensitive substrates. They are
sprayable as well. Further, they cure readily, especially by UV
radiation.
SUMMARY OF THE INVENTION
The present invention comprises randomly epoxidized star polymers,
based on at least one conjugated diolefin monomer, that contain
di-, tri- and/or tetrasubstituted olefinic epoxides. The polymers
of the invention may or may not be hydrogenated and if they are
hydrogenated, the hydrogenation may take place either before or
after epoxidation. The polymers may be crosslinked through at least
some of the epoxy functionality, preferably by radiation, and can
be used to make rapid curing and heat stable adhesives, sealants,
coatings, flexible printing plates, fibers and films, or used as
modifiers for asphalt, polyesters, polyamides and epoxies.
The star polymers have greater than four arms or branches.
Preferably, the polymers have more than eight arms, and most
preferably, more than twelve arms. Each arm has a molecular weight
from between 1,500 and 15,000, preferably from 2,000 to 10,000, and
most preferably from 3,000 to 7,000. The concentration of di-,
tri-, or tetrasubstituted olefinic epoxides (1,1-disubstituted,
1,2-disubstituted, 1,1,2-trisubstituted and
1,1,2,2-tetrasubstituted olefinic epoxides) is from 0.05 to 5
milliequivalents of epoxide per gram of polymer (Meq/g), preferably
from 0.1 to 3 Meq/g, and most preferably from 0.2 to 1 Meq/g.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a plot of viscosity data from Example 2 which shows the
relationship between the viscosities of the precursor and
epoxidized polymers.
DETAILED DESCRIPTION OF THE INVENTION
Polymers containing di-, tri or tetrasubstituted olefinic
unsaturation can be prepared by polymerizing one or more
polyolefins, particularly diolefins by themselves or with one or
more alkenyl aromatic hydrocarbon monomers. The polymers containing
such olefinic unsaturation may be prepared using anionic
initiators. Such polymers may be prepared using bulk, solution or
emulsion techniques.
A very useful embodiment of this invention may be conveniently
prepared by anionic polymerization, preparing arms D consisting of
homopolymers or copolymers of conjugated diene monomers or
copolymers of conjugated diene monomers and alkyl aryl monomers and
then coupling the arms to make a star polymer. The amount of alkyl
aryl monomers copolymerized in the D arms can be up to 99%,
provided that enough conjugated diene monomer is used to assure the
presence of a sufficient level of higher substituted olefinic
double bonds for epoxidation.
Preferably, the polymer is epoxidized under conditions that enhance
the epoxidation of the more highly substituted olefinic double
bonds, such as by the use of peracetic acid, wherein the rate of
epoxidation is generally greater the greater the degree of
substitution of the olefinic double bond (rate of epoxidation:
tetrasubstituted>trisubstituted>disubstituted>monosubstituted
olefinic double bond). Sufficient epoxidation is done to achieve
the desired level of epoxidation in the polymer (within the range
of 0.05 to 5 Meq/g). .sup.1 H NMR can be used to determine the loss
of each type of double bond and the appearance of epoxide.
If a substantially saturated polymer is desired, the epoxidized
polymer is hydrogenated to remove substantially all remaining
olefinic double bonds (ODB) and normally leaving substantially all
of the aromatic double bonds. Alternatively, selective partial
hydrogenation of the polymer may be carried out before epoxidation
such that from 0.05 to 5 Meq of olefinic double bonds are left
intact for subsequent epoxidation. In this case, the epoxidized
polymer may be partially hydrogenated in a selective manner with a
suitable catalyst and conditions (like those in Re 27,145, U.S.
Pat. No. 4,001,199 or with a titanium catalyst such as is disclosed
in U.S. Pat. No. 5,039,755, all of which are incorporated by
reference; or by fixed bed hydrogenation) that favor the
hydrogenation of the less substituted olefinic double bonds (rate
or hydrogenation:
monosubstituted>disubstituted>trisubstituted>tetrasubstituted
olefinic double bonds) and also leaves aromatic double bonds
intact, so as to leave some of the unsaturation intact in the D
arms (and/or any portions of the optional M block or the C arms,
discussed below, that may also contain unepoxidized higher
substituted olefinic double bonds). The epoxidation does not need
to be selective with respect to the degree of substitution on the
olefinic double bonds, since the objective is usually to epoxidize
as many of the remaining ODB's as possible.
Generally, if a hydrogenation step is used, sufficient improvement
of the polymer's chemical and heat stability should be achieved
justify the extra expense and effort involved. For greatest heat
stability, all of the olefinic double bonds, anyplace in the
polymer, that are not epoxidized should be removed so that less
than 1 Meq of ODB per gram of polymer remain, more preferably less
than 0.6 Meq/g, and most preferably less than about 0.3 Meq/g of
polymer.
In general, when solution anionic techniques are used, conjugated
diolefin polymers and copolymers of conjugated diolefins and
alkenyl aromatic hydrocarbons are prepared by contacting the
monomer or monomers to be polymerized simultaneously or
sequentially with an anionic polymerization initiator such as group
IA metals, their alkyls, amides, silanolates, napthalides,
biphenyls and anthracenyl derivatives. It is preferred to use an
organo alkali metal (such as sodium or potassium) compound in a
suitable solvent at a temperature within the range from about
-150.degree. C. to about 300.degree. C., preferably at a
temperature within the range from about 0.degree. C. to about
100.degree. C. Particularly effective anionic polymerization
initiators are organo lithium compounds having the general
formula:
wherein R is an aliphatic, cycloaliphatic, aromatic or
alkyl-substituted aromatic hydrocarbon radical having from 1 to
about 20 carbon atoms and n is an integer of 1 to 4.
Conjugated diolefins which may be polymerized anionically include
those conjugated diolefins containing from about 4 to about 24
carbon atoms such as 1,3-butadiene, isoprene, piperylene,
methylpentadiene, phenylbutadiene, 3,4-dimethyl-1,3-hexadiene,
4,5-diethyl-1,3-octadiene and the like. Isoprene and butadiene are
the preferred conjugated diene monomers for use in the present
invention because of their low cost and ready availability. The
conjugated diolefins which may be used in the present invention
include isoprene (2-methyl-1,3-butadiene), 2-ethyl-1,3-butadiene,
2-propyl-1,3-butadiene, 2-butyl-1,3-butadiene,
2-pentyl-1,3-butadiene (2-amyl-1,3-butadiene),
2-hexyl-1,3-butadiene, 2-heptyl-1,3-butadiene,
2-octyl-1,3-butadiene, 2-nonyl-1,3-butadiene,
2-decyl-1,3-butadiene, 2-dodecyl-1,3-butadiene,
2-tetradecyl-1,3-butadiene, 2-hexadecyl-1,3-butadiene,
2-isoamyl-1,3-butadiene,
2-phenyl-1,3-butadiene,2-methyl-1,3-pentadiene,2-methyl-1,3-hexadiene,
2-methyl-1,3-heptadiene, 2-methyl-1,3-octadiene,
2-methyl-6-methylene-2,7-octadiene (myrcene),
2-methyl-1,3-nonyldiene, 2-methyl-1,3-decyldiene, and
2-methyl-1,3-dodecyldiene, as well as the 2-ethyl, 2-propyl,
2-butyl, 2-pentyl, 2-hexyl, 2-heptyl, 2-octyl, 2-nonyl, 2-decyl,
2-dodecyl, 2-tetradecyl, 2-hexadecyl, 2-isoamyl and 2-phenyl
versions of all of these dienes. Also included are 1,3-butadiene,
piperylene, 4,5-diethyl-1,3-octadiene and the like. Di-substituted
conjugated diolefins which may be used include
2,3-dialkyl-substituted conjugated diolefins such as
2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-pentadiene,
2,3-dimethyl-1,3-hexadiene, 2,3-diethyl-1,3-heptadiene,
2,3-dimethyl-1,3-octadiene and the like and 2,3-fluoro-substituted
conjugated diolefins such as 2,3-difluoro-1,3-butadiene,
2,3-difluoro-1,3-pentadiene, 2,3-difluoro-1,3-hexadiene,
2,3-difluoro-1,3-heptadiene, 2,3-fluoro-1,3-octadiene and the like.
Alkenyl aromatic hydrocarbons which may be copolymerized include
vinyl aryl compounds such as styrene, various alkyl-substituted
styrenes, alkoxy-substituted styrenes, vinyl napthalene,
alkyl-substituted vinyl napthalenes and the like.
Conjugated dienes can also be copolymerized with methacrylates,
such as t-butyl methacrylate, as described in U.S. Pat. No.
5,002,676, which is incorporated herein by reference, and such
copolymers can be epoxidized and hydrogenated as described herein.
The preferred use position in the polymer for methacrylates, when
used, is in the C arms.
There are a wide variety of coupling agents or initiators that can
be employed. Any polyfunctional coupling agent which contains more
than four reactive sites can be employed. Examples of the types of
compounds which can be used are disclosed in U.S. Pat. No.
4,096,203, herein incorporated by reference, and include the
polyepoxides, polyisocyanates, polyimines, polyaldehydes,
polyketones, polyanhydrides, polyhalides, and the like. These
compounds can contain two or more types of functional groups such
as the combination of epoxy and aldehyde groups, isocyanate and
halide groups, and the like. Many suitable types of these
polyfunctional compounds have been described in the literature.
Coupling monomers are coupling agents where several monomer units
are necessary for every chain end to be coupled. Divinylbenzene
(DVB) is the most commonly used coupling monomer and results in
star polymers.
In general, any of the solvents known in the prior art to be useful
in the preparation of such polymers may be used. Suitable solvents,
then, including straight- and branched chain hydrocarbons such as
pentane, hexane, heptane, octane and the like, as well as,
alkyl-substituted derivatives thereof; cycloaliphatic hydrocarbons
such as cyclopentane, cyclohexane, cycloheptane and the like, as
well as alkyl-substituted derivatives thereof; aromatic and
alkyl-substituted derivatives thereof; aromatic and
alkyl-substituted aromatic hydrocarbons such as benzene,
napthalene, toluene, xylene and the like; hydrogenated aromatic
hydrocarbons such as tetraline, decalin and the like; linear and
cyclic ethers such as methyl ether, methylethyl ether, diethyl
ether, tetrahydrofuran and the like.
More specifically, the polymers of the present invention are made
by the anionic polymerization of conjugated diene monomers and
alkenyl aromatic hydrocarbon monomers in a hydrocarbon solvent at a
temperature between 0 and 100.degree. C. using an alkyl lithium
initiator. The living polymer chains are usually coupled by
addition of divinyl monomer to form a star polymer. Additional
monomers may or may not be added to grow more arms, C arms, or to
terminally functionalize, such as with ethylene oxide or carbon
dioxide to give hydroxyl or carboxyl groups, respectively, and the
polymer and the living chain ends are quenched with a proton source
such as methanol or hydrogen. Polymerization may also be initiated
from monomers such as m-divinylbenzene and m-diisopropenylbenzene
treated with butyl lithium.
The polymers can be either symmetric or asymmetric star (centrally
branched) polymers of the basic formula (A--M.sub.p).sub.n
--X--C.sub.r, wherein A is the diene containing block, M is an
optional miniblock and C is an optional arm (branch) consisting of
one or more blocks. The A--M.sub.p arms (branches) are referred to
as D arms when it is convenient to do so. The blocks themselves may
be homopolymer or copolymer blocks.
M is a miniblock of monomer that can be used to affect the number
or stability of the arms coupled or originating at X. The molecular
weight of M is greater than 50 and less than 1000. M is a vinyl
aromatic hydrocarbon or a diene, typically oligostyrene or
oligoisoprene. For instance, when coupling anionically prepared
A.sup.- living arms, where A is polybutadiene, with commercial
DVB-55 the degree of coupling to make the star is often less than
80%, with greater than 20% of the arms remaining unattached to the
main star mode in the final product. The exact amount left
unattached is very dependent upon the exact conditions of the
coupling reaction, such as the amount of ether cosolvent used, the
time elapsed after polymerization of the A blocks and the
temperature of the polymer solution during the DVB-55 addition. In
contrast, when a small miniblock of oligoisoprene is incorporated
to make the A--M arm (D), the coupling reaction is less sensitive
to reaction conditions and higher degrees of coupling can be
achieved. Further, presence of the miniblock can be additionally
beneficial when the polymer is being used under harsh service
conditions, such as high temperature use, because a completely
saturated block like oligostyrene or an epoxidized oligoisoprene
may prevent scission of the arm from the star at the core of the
star.
X sits at the junction point or region in the polymer molecule at
which the arms (branches) of the polymer connect and represents the
agent or agents that function as the connector. Generally X either
represents coupling agents or monomers that cause the majority of
the arms to join together after polymerization of the arms, or
represents an initiator with an active functionality greater than 4
from which polymerization of the arms takes place.
Asymmetric star polymers, by definition, require the use of the
optional C arms, which are necessarily different than the D arms
either in composition or molecular weight or both. C arms are
segments that are usually prepared from one or more of the monomers
used to prepare the D arms. The molecular weight of a C arm is from
50 to 15,000, preferably 500 to 10,000. The linear size of arms of
greater length gives polymers with high application viscosities.
Sometimes it is useful to prepare C from monomers other than those
used in D. For instance, a methacrylate monomer, such as t-butyl
methacrylate, can be added to a DVB coupled star prior to
termination and the arms C can be grown out from the living DVB
core of the star. Also, C can be formed from a polyvinyl aromatic
hydrocarbon. Combinations of the monomers can also be in C.
The subscripts are integers that indicate how many times a
particular arm or miniblock is present on a particular polymer. The
subscript p is 0 or 1, n and r are integers where n.gtoreq.2,
r.gtoreq.0, and n+r is the total number of arms and ranges from 5
to 100, preferably from 8 to 60, and most preferably from 12 to 40.
When p equals 0 or r equals 0 there is no miniblock M or no C arms.
Preferably n.gtoreq.r.
As the number of arms increases, so does the average molecular
weight of the polymer, which substantially increases the polymers
ability to cure easily, such as with very low dose radiation,
because the number of cure sites (epoxide sites) increases in
proportion to the molecular weight at any fixed concentration of
epoxide in the polymer. Fortunately, the substantially increased
polymer molecular weight causes very little increase in viscosity
because of the compact nature of a star polymer. However, trying to
attain the highest possible number of arms on a star polymer
results in the formation of some gel during the manufacture of the
polymer, which may make subsequent processing and filtering of the
polymer during manufacture, light scattering analysis for molecular
weight, or application of the polymer difficult or impossible. This
is why the most preferred upper bound for the number of arms is
40.
A special case is where A is a polyisoprene block polymerized under
conditions that yields primarily, i.e. at least 50%,
1,4-polyisoprene, for which the residual double bonds are
trisubstituted. Other special cases are where A is primarily
1,4-butadiene, a copolymer of primarily polyisoprene and butadiene
or where the A block is a random polyisoprene/polystyrene copolymer
in which a majority of the polyisoprene is 1,4-polyisoprene. D arms
may be made from a copolymer of isoprene and butadiene and the
isoprene can be preferentially epoxidized. Isoprene and butadiene
arms may be made in two different reactors and then blended and
coupled with DVB to make an asymmetric star polymer (other methods
may be used to make such polymers). Either epoxidation alone,
epoxidation first followed by hydrogenation, or partial
hydrogenation of these polymers first followed by epoxidation,
works extremely well. When A is polybutadiene, it often is
convenient to use a miniblock M where M is oligoisoprene or
oligostyrene. Star polymers are normally made by a coupling
reaction using divinyl monomer such as divinylbenzene. Like any
coupling reaction, it does not go to 100% completion and some
unattached arms will be present. The value of n is determined after
the polymer is made. The best way to assign the n values is to
measure the weight average molecular weight of the polymer by light
scattering as described below, including pure star and unattached
arms, subtract from it the portion of the mass due to the coupling
monomer and then divide this corrected weight average molecular
weight by the molecular weight of the arm which is usually the peak
molecular weight determined by GPC as described below.
Molecular weights of unassembled linear segments of polymers such
as arms of star polymers before coupling are conveniently measured
by Gel Permeation Chromatography (GPC), where the GPC system has
been appropriately calibrated. Polymers of known molecular weight
are used to calibrate and these must be of the same molecular
structure and chemical composition as the unknown linear polymers
or segments that are to be measured. For anionically polymerized
linear polymers, the polymer is essentially monodisperse and it is
both convenient and adequately descriptive to report the "peak"
molecular weight of the narrow molecular weight distribution
observed. Measurement of the true molecular weight of the final
coupled star polymer is not as straightforward or as easy to make
using GPC. This is because the star shaped molecules do not
separate and elute through the packed GPC columns in the same
manner as do the linear polymers used for the calibration, and,
hence, the time of arrival at a UV or refractive index detector is
not a good indicator of the molecular weight. A good method to use
for a star polymer is to measure the weight average molecular
weight by light scattering techniques. The sample is dissolved in a
suitable solvent at a concentration less than 1.0 gram of sample
per 100 milliliters of solvent and filtered using a syringe and
porous membrane filters of less than 0.5 microns pore size directly
into the light scattering cell. The light scattering measurements
are performed as a function of scattering angle and of polymer
concentration using standard procedures. The differential
refractive index (DRI) of the sample is measured at the same
wavelength and in the same solvent used for the light scattering.
The following references are herein incorporated by reference:
1. Modern Size-Exclusion Liquid Chromatography. M. W. Yau, J. J.
Kirkland, D. D. Bly, John Wiley & Sons, New York, N.Y.,
1979.
2. Light Scattering from Polymer Solutions, M. B. Huglin, ed.,
Academic Press, New York, N.Y. 1972.
3. W. Kay and A. J. Havlik, Applied Optics, 12, 541 (1973).
4. M. L. McConnell, American Laboratory, 63, May, 1978.
Each arm has a molecular weight from 1,500 to 15,000, preferably
2,000 to 10,000, and most preferably 3,000 to 7,000. These arm
molecular weights are very important to obtaining a low viscosity
polymer for ease of application. There are large viscosity
penalties to be paid if the arm length is either smaller than 1,500
or greater than about 15,000. It was totally unexpected that arm
lengths below 1,500 could far exceed viscosities at considerably
higher arm molecular weights. The range of 2,000 to 10,000 is
preferred because it greatly reduces the possibility of straying
into a much higher viscosity area, especially on the low arm
molecular weight side. The range of 3,000 to 7,000 is most
preferred because arms in this range will be at or very near the
absolute minimum in viscosity. Polymers of this invention based on
1,4-polybutadiene have similar or lower viscosity than similar
polymers based on 1,4-polyisoprene. It is also the case that
polymerizing to incorporate styrene, more 1,2-polybutadiene or more
3,4-polyisoprene, all of which raise the Tg of the A arms, will
cause the viscosity to rise at a fixed D arm molecular weight.
Upon epoxidation, the Meq of such epoxide per gram of the polymer
will be from 0.05 Meq/g to 5 Meq/g, preferably from 0.1 to 3 Meq/g
and most preferably 0.2 to 1 Meq/g. If there were greater
epoxidation, the polymers would over crosslink, have little
elasticity and be unsuitable for the applications intended. 0.2 to
1 Meq/g is preferred to obtain good UV curing and maintain pressure
sensitive properties.
Some other advantages of relatively low levels of epoxidation
are:
the manufacturing cost is lower because less epoxidizing agent is
used;
can maintain the polymer as an elastic material because the
crosslinking will not be dense; and
the polymer will be more hydrophobic so water will be less of a
problem for cationic curing.
The epoxidized copolymers of this invention can be prepared by the
epoxidation procedures as generally described or reviewed in the
Encyclopedia of Chemical Technology 19. 3rd ed., 251-266 (1980), D.
N. Schulz, S. R. Turner, and M. A. Golub, Rubber Chemistry and
Technology. 5, 809 (1982), W-K. Huang, G-H. Hsuie, and W-H. Hou,
Journal of Polymer Science. Part A: Polymer Chemistry, 26. 1867
(1988), and K. A. Jorgensen, Chemical Reviews, 89. 431 (1989), and
Hermann, Fischer, and Marz, Angew. Chem. Int. Ed. Engl. 30 (No.
12), 1638 (1991), all of which are incorporated by reference.
For instance, epoxidation of the base polymer can be effected by
reaction with organic peracids which can be preformed or formed in
situ. Suitable preformed peracids include peracetic and perbenzoic
acids. In situ formation may be accomplished by using hydrogen
peroxide and a low molecular weight fatty acid such as formic acid.
Alternatively, hydrogen peroxide in the presence of acetic acid or
acetic anhydride and a cationic exchange resin will form a peracid.
The cationic exchange resin can optionally be replaced by a strong
acid such as sulfuric acid or p-toluenesulfonic acid. The
epoxidation reaction can be conducted directly in the
polymerization cement (polymer solution in which the polymer was
polymerized) or, alternatively, the polymer can be redissolved in
an inert solvent such as toluene, benzene, hexane, cyclohexane,
methylenechloride and the like and epoxidation conducted in this
new solution or can be epoxidized neat. Epoxidation temperatures on
the order of 0 to 130.degree. C. and reaction times from 0.1 to 72
hours may be utilized. When employing hydrogen peroxide and acetic
acid together with a catalyst such as sulfuric acid, the product
can be a mixture of epoxide and hydroxy ester. The use of peroxide
and formic acid in the presence of a strong acid may result in
diolefin polymer blocks containing both epoxide and hydroxy ester
groups. Due to these side reactions caused by the presence of an
acid, it is preferable to carry out the epoxidation at the lowest
possible temperature and for the shortest time consistent with the
desired degree of epoxidation. Epoxidation may also be accomplished
by treatment of the polymer with hydroperoxides or oxygen in the
presence of transition metals such as Mo, W, Cr, V and Ag, or with
methyl-trioxorhenium/hydrogen peroxide with and without amines
present. .sup.1 H NMR is an effective tool to determine which and
how much of each type of ODB is epoxidized. Further, the amount of
epoxy can also be measured by the direct titration with perchloric
acid (0.1 N) and quaternary ammonium halogenide
(tetraethyl-ammonium bromide) where the sample is dissolved in
methylene chloride. Epoxy titration is described in Epoxy Resins
Chemistry and Technology, edited by Clayton A. May and published in
1988 (p. 1065) which is herein incorporated by reference.
An epoxidized polymer of the present invention can be further
derivatized by a subsequent reaction either separately or in-situ
to provide useful reactive elastomeric binders that have reactive
functionality other than the epoxy group. Examples of these
reactions are described by copending, commonly assigned
applications, "Hydroxyl Functional Derivatives of Epoxidized Diene
Polymers and Process for Making Them", U.S. Ser. No. 863,580 and
"Hydroxyl Functional Derivatives of Epoxidized Diene Polymers and
Process for Making Them (II)", U.S. Ser. No. 863,648, both filed on
Apr. 3, 1992, which are herein incorporated by reference. Epoxy
groups can be converted to hydroxyl functionality, capable of
crosslinking with amino-formaldehyde resins or isocyanates, by
reduction or reaction with water. Reaction with azide ion, reaction
with cyanotrimethylsilane followed by reduction or reaction with
dialkylaminosilanes, ammonia, or amines will give polymers
containing both amino and hydroxyl functionality that can be used
to enhance adhesion to cellulosic substrates or provide reactive
sites for isocyanate cure. Reaction with amino or mercapto acids
can be used to prepare polymers containing hydroxyl and carboxylic
acid functionality, providing greater adhesion to metals or to
basic polymers such as nylon. Reaction with mercaptosilanes can be
used to prepare polymers containing the elements of coupling
agents, providing excellent adhesion to glass. These functional
groups may also be introduced in the form of protected functional
groups by reaction of the epoxy with the appropriately
functionalized organometallic reagent (lithium organocuprates,
Grignard reagents). Hydroxyl and aldehyde functionality may also be
introduced by hydroformylation. Reactions with acrylamides and
acrylic acids will introduce sites for free radical grafting.
Further neutralization of the carboxylic acid or amine-containing
polymer with base or acid will give varying amounts of water
dispersability, depending on the level of functionality and
neutralization.
A partially hydrogenated, but not epoxidized, polymer of the
present invention can be further derivatized as well. Such a
polymer can be halogenated, for example, by reacting it with a
solution of HBr in acetic acid, or with chlorine (Cl.sub.2) or
bromine (Br.sub.2), either gaseous, or in solution. A wide variety
of species, including alcohols, carboxylic acids and nitriles, can
be added across the double bond in the presence of protic acids to
form the corresponding ethers, esters and amides. Acid chlorides
and anhydrides can be added across the double bond in the presence
of Lewis acids. A wide variety of species containing active
protons, including thiols, primary alcohols and amines, aldehydes
and species of the structure ZCH.sub.2 Z, where Z and Z are
electron withdrawing groups, such as NO.sub.2, CN, or CO.sub.2 H,
can be added across the double bond in the presence of radical
generators, such as organic peroxides. Hydroboration can be used to
prepare the alkylborane, as described in S. Ramakrishnan, E.
Berluche, and T. C. Chung, Macromolecules, 23, 378 (1990), and
subsequent papers by T. C. Chung. The alkylborane derivative may
then be transformed to the alcohol, or amine, or other functional
groups. Diazo compounds may be added to the double bonds, either
under the influence of heat, or metal catalysts, such as Cu and Rh
salts. Reactive dienophiles, such as maleic anhydride and
di-t-butyl azodicarboxylate can be added to the double bond to form
the anhydride or the hydrazide (which can be thermally converted to
the hydrazine), respectively. Reactive dipoles, such as nitrile
oxides and nitrones can be added to the double bond. Hydrogenation
of the above mentioned derivatives can be used to introduce
amino-alcohol functionality. A variety of oxidative reactions,
including oxidation with potassium permanganate and sodium
perborate, may be used to introduce hydroxyl groups.
The polymers of this invention are preferably cured (crosslinked)
by ultraviolet or electron beam radiation, but radiation curing
utilizing a wide variety of electromagnetic wavelengths is
feasible. Either ionizing radiation such as alpha, beta, gamma,
X-rays and high energy electrons or non-ionizing radiation such as
ultraviolet, visible, infrared, microwave and radio frequency may
be used. The details of radiation curing are given in commonly
assigned copending applications Ser. No. 692,839, filed Apr. 28,
1991, "Viscous Conjugated Diene Block Copolymers" and Ser. No.
772,172, filed Oct. 7, 1991, "Crosslinked Epoxy Functionalized
Block Polymers and Adhesives.
The most common sources of alpha, beta and gamma radiation are
radioactive nuclei. High voltage electron accelerators are
preferred over gamma radiation and certain types of X-ray
processing equipment. Commercially available high or low energy
electron-processing equipment are the Dynamitron.RTM. device,
dynacote, insulating-core transformer, linear accelerator, Van de
Graaff accelerator, pelletron, laddertron and linear cathode.
Ultraviolet light sources may be based on the mercury-vapor arc.
Visible light sources can be obtained from high pressure mercury
arcs by addition of rare gases or metal halides, which increase the
number of emission lines in the 350-600 mm region of the
spectrum.
The mechanism of the radiation crosslinking is believed to be
generation of cations by removal of an electron from the polymer
chain. The cation then readily reacts with an epoxy group, if an
epoxy group is available. This reaction results in an ether
crosslink between two polymer molecules and a new cation site on a
polymer which formerly contained the epoxy functionality. The new
cation will either propagate, forming another ether crosslink with
another epoxy oxygen, or terminate by recapturing an electron.
The presence of water in the polymeric composition during the
radiation crosslinking is very undesirable due to the tendency of
water to terminate the crosslinking. The radiation curing is
therefore generally more effective if the polymeric composition is
at temperature near or above the boiling point of water at the time
of the radiation curing.
The amount of radiation necessary for high gel formation varies
with the thickness of the polymeric mass being irradiated, the
amount of epoxy functionality, the extent to which the epoxy
functionality is concentrated in specific regions within the
polymeric mass and the type of radiation utilized. When electron
beam radiation is utilized, radiation doses of about 0.1 Mrads to
about 10 Mrads/s are acceptable and from about 0.1 Mrads to about 5
Mrads are preferred because of equipment cost and possible damage
to substrate material.
When using non-ionizing radiation it is necessary to employ a
photoinitiator to initiate the crosslinking reaction. Useful
photoinitiators include diarylidonium, alkoxy-substituted
diarylidonium, triarylsulfonium, dialkylphenacylsulfonium, and
dialkyl-4-hydrophenylsulfonium salts. The anions in these salts
generally possess low nucleophilic character and include
SbF.sub.6.sup.-, BF.sub.4.sup.-, PF.sub.6.sup.- and
AsF.sub.6.sup.-. Specific examples include
(4-octyloxyphenyl)-phenyl-iodonium hexafluoroantimonate, UVI-6990
(from Union Carbide). Bis(dodecylphenyl)iodonium
hexafluoroantimonate, UVI-6974 (Union Carbide), is especially
effective. The onium salts can be used alone or in conjunction with
a photosensitizer to respond to long wave length UV and visible
light. Examples of photosensitizers include thioxanthone,
anthracene, perylene, phenothiazione, 1,2-benzathracene coronene,
pyrene and tetracene. The photoinitiator and photosensitizer are
chosen to be compatible with the polymer being crosslinked and the
light source available.
Reactive (curable) diluents that can be added to the polymer
include epoxy, vinyl ether, alcohol, acrylate and methacrylate
monomers and oligomers. Such polymers and other diene-based
polymers may also be added or blended. Examples of epoxy reactive
diluents include bis(2,3-epoxycyclopentyl)ether (Union Carbide
EP-205), vinyl cyclohexene dioxide, limonene oxide, limonene
dioxide, pinene oxide, epoxidized fatty acids and oils like
epoxidized soy and linseed oils.
The polymers may also be cured without the use of radiation by
addition of a cationic initiator. Suitable initiators include the
halides of tin, aluminum, zinc, boron, silicon, iron, titanium,
magnesium and antimony, and the fluoroborates of many of these
metals. BF.sub.3 complexes such as BF.sub.3.sup.-, ether and
BF.sub.3 -amine, are included. Also useful are strong Bronsted
acids such as trifluoromethanesulfonic (triflic acid) and the salts
oftriflic acid such as FC-520 (3M Company). The cationic initiator
is chosen to be compatible with the polymer being crosslinked, the
method of application and cure temperature. The epoxy-containing
polymers may also be crosslinked by the addition of multifunctional
carboxylic acids, acid anhydrides, and alcohols, and in general by
the curing methods described in U.S. Pat. No. 3,970,608, which is
incorporated by reference. Volatile amines can be used to inhibit
or retard unwanted cure, such as to maintain fluidity in one pack
formulations until they are applied and reach the appropriate bake
temperature for cure. They may also be cured by use of amino resins
in the presence of a proton donating acid such as is described in
"Method of Chemically Crosslinking Sterically Hindered Epoxidized
Polymers", U.S. Ser. No. 863,644, filed Apr. 3, 1992, which is
copending and commonly assigned. The polymers may thus be cured by
using from 0.5 to 40 percent of the weight of the polymer of an
amino resin, such as a glycoluril-formaldehyde resin or a
urea-formaldehyde resin, and from 0.1 to 4 percent of the weight of
the polymer of a proton-donating acid catalyst such as mineral
acids, p-toluene sulfonic acid, dinonyl naphthalene disulfonic
acid, dodecylbenzene sulfonic acid, oxalic acid, maleic acid,
hexamic acid, phosphoric acid, dimethyl acid pyrophosphate,
phthalic acid, acrylic acid and a diethyl ammonium salt of
trifluoromethane sulfonic acid. The curing is carried out for from
5 seconds to 30 minutes at a temperature of from -5.degree. C. to
400.degree. C. Radiation crosslinking is preferred because reactive
ingredients do not come in contact with warm adhesives.
The crosslinked materials of the present invention are useful in
adhesives (including pressure sensitive adhesives, contact
adhesives, laminating adhesives and assembly adhesives), sealants,
coatings, films(such as those requiring heat and solvent
resistance), printing plates, fibers, and as modifiers for
polyesters, polyethers and polyamides. The polymers are also useful
in asphalt modification. In addition to the functionalized polymer
and any curing aids or agents, products formulated to meet
performance requirements for particular applications may include
various combinations of ingredients including adhesion promoting or
tackifying resins, plasticizers, fillers, solvents, stabilizers,
etc. as described in detail in the aforementioned commonly assigned
applications which are incorporated by reference.
Compositions of the present invention are typically prepared by
blending the components, preferably between 25.degree. C. and
125.degree. C., until a homogeneous blend is obtained, usually less
than three (3) hours. Various methods of blending are known to the
art and any method that produces a homogeneous blend is
satisfactory. The resultant compositions may then preferably be
used in a wide variety of applications. Alternatively, the
ingredients may be blended into a solvent.
Adhesive compositions of the present invention may be utilized as
many different kinds of adhesives' for example, laminating
adhesives, flexible packaging laminated adhesives, pressure
sensitive adhesives, tie layers, hot melt adhesives, solvent borne
adhesives and waterborne adhesives in which the water has been
removed before curing. The adhesive can consist of simply the
epoxidized polymer or, more commonly, a formulated composition
containing a significant portion of the epoxidized polymer along
with other known adhesive composition components. A preferred
method of application will be warm melt application at a
temperature 20 to 125.degree. C. because warm melt application is
non-polluting and can be used on heat sensitive substrates. The
adhesive can be heated before and after cure to further promote
cure or post cure. Radiation cure of warm adhesive is believed to
promote faster cure than radiation cure at room temperature.
Preferred uses of the present formulation are in the preparation of
pressure-sensitive adhesive tapes and the manufacture of labels or
flexible packaging. The pressure-sensitive adhesive tape comprises
a flexible backing sheet and a layer of the adhesive composition of
the instant invention coated on one major surface of the backing
sheet. The backing sheet may be a plastic film, paper or any other
suitable material and the tape may include various other layers or
coatings, such as primers, release coatings and the like, which are
used in the manufacture of pressure-sensitive adhesive tapes.
Alternatively, when the amount of tackifying resin is zero, the
compositions of the present invention may be used for adhesives
that do not tear paper and molded goods and the like.
EXAMPLE 1
Polymer 1 was a symmetric star polymer D.sub.n --X, with
polyisoprene arms, D, prepared by anionic polymerization. The
polymer was prepared as follows. Isoprene monomer was fed to a
reactor already charged with cyclohexane and sec-butyl lithium
initiator, and the isoprene was completely polymerized to form the
arms. DVB-55 was added to couple the arms, and after about one hour
reaction time, methanol was added to terminate the living polymer.
0.102 pounds of the DVB-55 mixture (a product of Dow Chemical,
containing about 55-56 wt. % divinylbenzene and about 42 wt. %
ethylvinylbenzene) was used for every 1.000 pound of isoprene
monomer. A sample was taken from the reactor just before the
addition of the DVB-55, and was analyzed by GPC to determine the
peak molecular weight of the polyisoprene arms. A value of 6820 was
found. Thus, each arm consisted of about 100 isoprene mers, and
about 5.3 mers of the DVB-55 monomer mixture per polyisoprene arm
were used to couple and form the star polymer. GPC on the final
star polymer indicated that the polymer was 92% coupled. The weight
average molecular weight, M.sub.w, of the polymer was measured be
static light scattering. Dry polymer was dissolved in
tetrahydrofuran and filtered through a 0.2 micron filter. The
analysis wavelength was 632.8 nm, the temperature was 25.0.degree.
C. and the DRI was 0.135. The M.sub.w determined was 157,000.
Hence, the average number of arms on the polymer was 21. .sup.1 H
NMR on the final polymer indicated the arms consisted of 94%
1,4-polyisoprene and 6% 3,4-polyisoprene. The majority of the
polymer was left in solution for epoxidations. The % polymer solids
of the solution was determined to be 23.3%.
EXAMPLE 2
Preparation of polymers 2-9. These polymers were made by
epoxidizing portions of Polymer 1 from Example 1 with peracetic
acid (in a stirred glass flask with acid dripped in slowly and the
reaction temperature was 60.degree. C. and the reaction hold time
was 3.5 hours) according to the recipes in Table 1 below.
TABLE 1
__________________________________________________________________________
Polymer (gram recipes) Polymer 2 3 4 5 6 7 8 9
__________________________________________________________________________
Polymer 1 solution 2505 1812 1003 136320 1812 1003 1812 1003 (23.3%
polymer) 0.1 N NaOH 13 19 10 1690 32 18 45 25 peracetic acid
solution 63 92 51 8284 156 86 220 122 Meq epoxide per gram of
polymer Theoretical Basis Polymer 1 0.50 1.00 1.00 1.20 1.70 1.70
2.40 2.40 Basis final epoxidized 0.49 0.98 0.98 1.18 1.66 1.66 2.31
2.31 polymer Experimental By .sup.1 H NMR on epoxidized 0.45 1.06
1.07 1.17 1.74 1.89 2.88 2.72 polymer
__________________________________________________________________________
Each polymer solution was completely neutralized with an equal
volume of aqueous NaOH wash solution. The mixtures were stirred for
about 30 minutes, agitation was stopped and the bottom water/sodium
acetate layers were removed. Each of the polymer solutions were
washed at least three more times with distilled water to remove
residual sodium acetate. Polymers 3 and 4 were blended while still
in solution to make a larger batch, designated polymer 10.
Likewise, polymers 6 and 7, and polymers 8 and 9 were blended to
make polymers designated polymer 11 and polymer 12, respectively. A
small amount of a phenolic antioxidant was added to each polymer
solution and then polymers 2, 3, 10, 11, and 12 were dried in a
vacuum oven to remove the solvent.
The viscosities of Polymers 1, 2, 5, 10, 11 and 12 were measured
using a Rheometrics Dynamic Mechanical Spectrometer with a parallel
plate geometry. The measurements were made in dynamic mode at a
shear rate of 10 radians per second and temperatures from 25 to
70.degree. C. as shown in FIG. 1. FIG. 1 demonstrates that the low
level of epoxidation in Polymer 2 (0.45 meg epoxide per gram) does
not significantly change the viscosity from the basis Polymer 1.
Higher levels of epoxidation in Polymers 5, 10, 11 and 12 show
increased viscosity over the basis Polymer 1. All 6 polymers shown
in FIG. 1 have similar reductions in viscosity with increasing
temperature. Viscosity falls by a factor of approximately 10.times.
for each 40.degree. C. of temperature increase.
EXAMPLE 3
Polymer 13 was prepared by partially hydrogenating Polymer 1 using
a nickel-aluminum catalyst under conditions that do not hydrogenate
aromatic double bonds. The catalyst was washed out. The
hydrogenation catalyst was made by the reaction of nickel
2-ethylhexanoate and triethylaluminum (Al/Ni ratio was about 2.3/1)
and was used at 202 ppm nickel on a solution basis, at a pressure
of 800 psi and a temperature ranging from 60 to 80.degree. C.
.sup.1 H NMR analysis was used to obtain experimental values for
the residual olefinic double bonds left in the polymer.
______________________________________ Meq epoxide/g polymer
______________________________________ 1,4-polyisoprene
(trisubstituted ODB) 2.03 3,4-polyisoprene (disubstituted ODB) 0.02
total = 2.05 ______________________________________
EXAMPLE 4
Preparation of polymer 14. Polymer 14 was made by epoxidizing a
portion of polymer 13 from Example 3 with peracetic acid according
to the procedure of Example 2 and the recipe below.
______________________________________ Polymer 14 (gram recipe)
______________________________________ Polymer 1 solution 2342
(23.3% polymer) 0.1 N NaOH 50 peracetic acid 246 solution Meq
epoxide per gram of polymer Theoretical Basis Polymer 1 2.04 Basis
final 1.98 epoxidized polymer Experimental By .sup.1 H NMR on 1.95
epoxidized polymer ______________________________________
The polymer solution was completely neutralized with an equal
volume of an aqueous NaOH was solution, and then water washed to
remove residual sodium acetate. A small amount of a phenolic
antioxidant was added to the polymer solution and then the polymer
14 was dried in a vacuum oven to remove the solvent.
EXAMPLE 5
Polymer 15 was a symmetric star polymer, D.sub.n --X, with
polyisoprene arms, D, prepared by anionic polymerization. The
polymer was prepared as follows. Isoprene monomer was fed to a
reactor already charged with cyclohexane and sec-butyl lithium
initiator, and the isoprene was completely polymerized to form the
arms. DVB-55 was added to couple the arms, and after about one hour
reaction time, methanol was added to terminate the living polymer.
0.129 pounds of the DVB 55 mixture was used for every 1.000 pound
of isoprene monomer. A sample was taken from the reactor just
before the addition of the DVB-55, and was analyzed by GPC to
determine the peak molecular weight of the polyisoprene arms. A
value of 3030 was found. Thus, each arm consisted of about 44
isoprene mers, and about 2.9 mers of the DVB-55 monomer mixture per
polyisoprene arm were used to couple and form the star polymer. GPC
on the final star polymer indicated that the polymer was 74%
coupled. The weight average molecular weight, M.sub.w, of the
polymer was measured be static light scattering. Dry polymer was
dissolved in tetrahydrofuran and filtered, with considerable
difficulty, through a 0.2 micron filter. The analysis wavelength
was 632.8 nm, the temperature was 25.0.degree. C. and the DRI was
0.135. The M.sub.w determined was 198,000, but the value is not
considered to be precise because of the experimental difficulties.
Hence, the average number of arms on the polymer was about 58.
.sup.1 H NMR on the final polymer indicated the arms consisted of
94% 1,4-polyisoprene and 6% 3,4-polyisoprene. The polymer was dried
to remove the solvent.
EXAMPLE 6
Preparation of polymer 16. Polymer 16 was made by epoxidizing a
portion of polymer 15 from Example 5 with peracetic acid according
to the recipe below.
______________________________________ Polymer 16 (gram recipe)
______________________________________ Polymer 15 69 (23.3%
polymer) Cyclohexane 128 Sodium carbonate 0.32 peracetic acid 15
solution Meq epoxide per gram of polymer Theoretical Basis Polymer
1 1.00 Basis final 0.98 epoxidized polymer Experimental By .sup.1 H
NMR on 0.80 epoxidized polymer
______________________________________
After neutralizing and water washing, a small amount of a phenolic
antioxidant was added to the polymer solution, and polymer 16 was
dried in a vacuum oven to remove the solvent.
EXAMPLE 7
Polymer 1 and polymer 10 were compared for ability to cure by UV
irradiation. The following formulations were prepared. Zonatac 105
lite is a polyterpene tackifying resin from Arizona Chemical.
Cyracure UVI-6974 is a photoinitiator (50 percent mixed
triarylsulfonium hexafluoroantimonate salts and 50 percent
propylene carbonate) made by Union Carbide.
______________________________________ Formulation 7-A 7-B 7-C
______________________________________ Polymer 1 100 30 0 Polymer
10 0 70 70 Zonatac 105 lite 0 0 30 Cyracure UVI-6974 0.93 0.93 0.93
Tetrahydrofuran 67 67 67 ______________________________________
After all the components of the formulation were dissolved, films
were cast onto 1 mil polyester film to give about 1.5 mils of
coating when dried. The films were very sticky to the touch and
lacked cohesive strength. The test films were prebaked for 2
minutes at 121.degree. C. and then were irradiated with UV light
from a Linde Photocure unit equipped with aluminum reflectors and
one medium pressure Hg bulb. The films passed under the lamp at 30
feet per minute with the test formulation facing the incoming UV
light. All three of the films remained sticky to the finger and had
not developed good cohesive strength for at least 5 minutes after
the UV treatment; they should have been good for laminating
flexible backings. The films were then give a post thermal
treatment of 10 minutes in a 121.degree. C. oven. After this
postcure, formulation 7-A still had not developed good cohesive
strength, and 7-B was little better, whereas 7-C was tacky but had
excellent cohesive strength. Each of the postbaked test films were
measured for polymer gel content with the following results.
______________________________________ Formulation Polymer Gel, %
______________________________________ 7-A 1 7-B 12 7-C 75
______________________________________
The gel data clearly shows that the unepoxidized star polymer 1 did
not cure, and when blended in (at the 30% level) with polymer 10,
retards the cure of epoxidized polymer 10. Whereas, formulation 7-C
shows that the use of the polyterpene tackifying resin, Zonatac 105
lite at the 30% level, does not prevent epoxidized polymer 10 from
curing sufficiently to provide good cohesive strength.
EXAMPLE 8
A portion of polymer 10 containing 1% Cyracure UVI-6974 was
dissolved in THF and cast onto pieces of 1 mil polyester film. The
dried film thickness was about 1.5 mils. The films were examined
for gel content as a function of the curing treatments shown. In
all cases the films were prebaked for 2 minutes in a 121.degree. C.
oven before the treatment, and were aged under ambient conditions
for 1 day before starting the gel test.
______________________________________ Treatment Gel Content, %
______________________________________ Bake for 10 minutes in a
121.degree. C. oven. 1 UV exposure at 99 fpm with Vycor 63 filter
in place. UV exposure at 99 fpm with Vycor 98 filter in place,
followed by 10 minutes in a 121.degree. C. oven.
______________________________________
The results show how a polymer like polymer 10 can be applied warm
without causing gel formation, and then can be activated by
exposure to very low levels of UV light and will cure under ambient
conditions with time, and how cure can be accelerated by
application of mild heating. The action of the Vycor filter in the
experiment was to reduce the effective amount of light reaching the
substrate from the single medium pressure Hg bulb by a factor of
about 4, so as to simulate the amount of UV light that would be
seen at about 400 fpm if the filter is not in place.
EXAMPLE 9
Portions of polymers 2, 10, and 12 were dissolved in toluene and
thin films were cast onto 1 mil polyester film. Dry film thickness
of each polymer on the polyester film was about 1.5 mils. The films
were prebaked for 2 minutes in a 121.degree. C. oven to assure
complete dryness, and were then cured with 3 Mrads of EB
irradiation from an Energy Sciences CB-150 EB processor. The test
films were measured for degree of cure (gel content) and for
several typical pressure sensitive adhesive properties. All three
of the polymers cured well to give strong films with good
properties.
______________________________________ Polymer 2 10 12
______________________________________ Epoxidation level, Meq/g
0.45 1.07 2.80 (measured) Gel Content, % 83 85 87 Rolling Ball
Tack, cm 1 2 2 Polyken Probe Tack, g 600 224 543 Shear Adhesion
Failure 123 139 143 Temperature, .degree.C. (1 in* 1 in lap, 1000
g) 95.degree. C. Holding Power, min >1000 >1000 >1000 (1
in* 1 in lap, 1000 g) ______________________________________
The SAFT was measured by 1".times.1" Mylar to Mylar lap joint with
a 1 kg weight. SAFT (shear adhesion failure temperature) measures
the temperature at which the lap shear assembly fails underload in
an oven whose temperature is raised at a rate of 40.degree. F. per
hour. Rolling Ball Tack (RBT) is the distance in centimeters a
steel ball rolls on the adhesive film with a standard initial
velocity (PSTC test No. 6). Small numbers indicate aggressive tack.
95.degree. C. Holding Power is the time required to pull a standard
area (1".times.1") of tape from a standard Mylar test surface under
a standard load kg), in shear at 2.degree. antipeel. Polyken probe
tack (PPT) was determined by ASTM D-2979. For HP and PPT, higher
numbers indicate better performance for most pressure sensitive
adhesive applications.
EXAMPLE 10
Portions of polymer 10 and polymer 12, each with 1% Cyracure
UVI-6974 added, were dissolved in THF and cast onto flexible 1 mil
polyester film. The polymer film thickness after evaporation of the
THF was about 1.5 mils. The films were prebaked for 2 minutes in a
121.degree. C. oven, UV cured at 30 fpm with no Vycor filter used,
and postbaked for 10 minutes in a 121.degree. C. oven. The films
were tested for polymer gel formation and typical pressure
sensitive adhesive properties.
______________________________________ Polymer 10 12
______________________________________ Epoxidation level, Meq/g
1.07 2.80 (measured) Polymer Gel Content, % 99 98 Rolling Ball
Tack, cm 4 >12 Polyken Probe Tack, g 221 8 Shear Adhesion
Failure 98 105 Temperature, .degree.C. (1 in* 1 in lap, 1000 g)
95.degree. C, Holding Power, min >1000 >1000 (1 in* 1 in lap,
1000 g) ______________________________________
The results show that polymer 10 is a much better pressure
sensitive adhesive than polymer 12. Polymer 12 has a higher level
of epoxidation and cures too much, by UV, to make as good a
pressure sensitive adhesive as polymer 10.
EXAMPLE 11
Resin 17 (epoxidized S10) was prepared from Piccolyte S-10
polyterpene resin from Hercules in a manner similar to that used to
prepare the epoxidized star polymers above (temperature ranged from
19 to 54.degree. C. and the hold time was 1.75 hours).
______________________________________ Resin 17 (gram recipe)
______________________________________ Piccolyte S-10 479
Cyclohexane 930 Sodium carbonate 6.3 peracetic acid 293 Meq epoxide
per gram of polymer Experimental 0.6 by epoxy titration epoxidized
resin ______________________________________
The resin solution was completely neutralized with an equal volume
of an aqueous NaOH wash solution, and then water washed to remove
residual sodium acetate. The resin solution was mixed with
magnesium sulfate to remove any residual water and the magnesium
sulfate was filtered out. The resin solution was vacuum dried to
remove the solvent.
The following adhesive formulations were made using polymer 5 with
Piccolyte S-10 and resin 17.
______________________________________ Formulation 11-A 11-B
______________________________________ Polymer 5 75 75 Piccolyte
S-10 25 0 Resin 17 0 25 Cyracure UVI-6974 1 1 Irganox 1010
(antioxidant) 1 1 Tetrahydrofuran 70 70
______________________________________
Formulations 11-A and 11-B were cast on 1 mil polyester film to
give about 1.5 mils when dry. The test films were prebaked for 2
minutes in a 121.degree. C. oven, UV irradiated at 30 fpm using no
Vycor filter, and then immediately postbaked for 10 minutes in a
121.degree. C. oven. The films of both test formulations remained
soft and gooey immediately after the UV exposure. They developed
excellent cohesive strength during the postbake. The films were
tested for polymer gel content and PSA properties after the
cure.
______________________________________ Formulation 11-A 11-B
______________________________________ Polymer Gel Content, % 100
100 Formulation Gel Content, % 76 84 Rolling Ball Tack, cm >16 6
Polyken Probe Tack, g 0 202 95.degree. C. Holding Power 4 480 (1
in* 1 in, 500 g), min Room Temperature Holding >4000 >4000
Power to Steel, min (1 in* 1 in, 500 g)
______________________________________
The results above show the advantage of using an epoxidized
polyterpene resin over the unepoxidized resin for improved
adhesion. With UV cure the epoxidized polyterpene resin appears to
have advanced in molecular weight and partially joined the
polymeric gel network.
EXAMPLE 12
This example shows the ability of different resins to tackify
polymer 14.
__________________________________________________________________________
Formulation 12 A B C D E F G H I K
__________________________________________________________________________
Polymer 14 100 75 75 75 75 75 75 75 75 75 Piccolyte S-10 0 25 0 0 0
0 0 0 0 0 Resin 17 0 0 25 0 0 0 0 0 0 0 Regalrez 1094 0 0 0 25 0 0
0 0 0 0 Escorez 5380 0 0 0 0 25 0 0 0 0 0 Arkon P90 0 0 0 0 0 25 0
0 0 0 Piccolyte S70 0 0 0 0 0 0 25 0 0 0 Foral 85 0 0 0 0 0 0 0 25
0 0 Piccolyte A-11 0 0 0 0 0 0 0 0 25 0 Piccolyte C-11 0 0 0 0 0 0
0 0 0 25 Toluene 63 63 63 63 63 63 63 63 63 63
__________________________________________________________________________
The test films were exposed to 3 Mrad of EB radiation and tested
for pressure sensitive adhesive properties. Regalrez 1094 is a
hydrogenated resin from Hercules. Escorez 5380 is a hydrogenated
resin from Exxon Chemical. Arkon P90-resin from Arakawa Chemical.
Piccolyte S70 is a polyterpene resin from Hercules, as are
Piccolyte A-115 and C-115. Floral 85 resin is from Hercules.
__________________________________________________________________________
Formulation 12 A B C D E F G H I J
__________________________________________________________________________
Polymer Gel, % 90 80 66 85 82 87 -- 66 70 75 Rolling Ball Tack, cm
9 3 2 3 4 5 -- 2 4 9 Polyken Probe Tack, g 132 362 490 308 382 330
-- 908 965 541 180.degree. peel from steel, 0.2 0.5 1.5 0.7 0.5 0.6
-- 1.8 2.0 2.0 pli
__________________________________________________________________________
180.degree. peel is determined by PSTC test No. 1.
EXAMPLE 13
Polymer 18 was a symmetric star polymer, D.sub.n --X, with
polyisoprene arms, D, prepared by anionic polymerization.
Preparation was almost identical to that of polymer 1. Polymer 18
was prepared as follows. Isoprene monomer was fed to a reactor
already charged with cyclohexane and sec-butyl lithium initiator,
and the isoprene was completely polymerized to form the arms.
DVB-55 was added to couple the arms, and after about one hour
reaction time, methanol was added to terminate the living polymer.
0.102 pounds of the DVB-55 mixture (a product of Dow Chemical,
containing about 55-56 wt. % divinylbenzene and about 42 wt. %
ethylvinylbenzene) was used for every 1.000 pound of isoprene
monomer. A sample was taken from the reactor just before the
addition of the DVB-55, and was analyzed by GPC to determine the
peak molecular weight of the polyisoprene arms. A value of 4800 was
found. Thus, each arm consisted of about 70 isoprene mers, and
about 3.7 mers of the DVB-55 monomer mixture per polyisoprene arm
were used to couple and form the star polymer. GPC on the final
star polymer indicated that the polymer was 75% coupled. The weight
average molecular weight, M.sub.w, of the polymer was measured be
static light scattering. Dry polymer was dissolved in
tetrahydrofuran and filtered through a 0.2 micron filter. The
analysis wavelength was 632.8 nm, the temperature was 25.0.degree.
C. and the DRI was 0.135. The M.sub.w determined was 85,000. Hence,
the average number of arms polymer was 16. .sup.1 H NMR on the
final polymer indicated the arms consisted of 94% 1,4-polyisoprene
and 6% 3,4 polyisoprene.
EXAMPLE 14
Polymer 19 was a symmetric star polymer with polyisoprene arms.
This polymer was prepared by an anionic process similar to that
used in the synthesis of Polymer 1. The principle differences in
this experiment were that the polymerization solvent was a mixture
of cyclohexane/diethyl ether (9/1 wt/wt) and the coupling agent was
DVB-80 (Dow Chemical) (m- & p-divinylbenzene, 78% wt,
ethylvinylbenzene, 20% wt, diethylbenzene, 1% wt, naphthalene, 1%
wt). In this example, the polyisoprene arm, before reaction with
DVB, was found by NMR analysis to have a molecular weight (MW) of
1200 (1,4-addition=58%; 3,4-addition=42%). The living polyisoprene
was coupled with DVB (DVB/Isoprene=0.526 wt/wt) affording a
symmetrical star polymer. Analysis of the coupled polymer by GPC
found essentially all of the polyisoprene arms were coupled to DVB
cores. The polymer solution was quenched with water to remove any
living chain ends that might have been present, washed repeatedly
to remove lithium salts and concentrated to remove solvent. The
polymer was isolated as a white solid and reserved for rheology
studies.
Polymer 20 was a symmetric star polymer with polyisoprene arms.
This polymer was prepared by an anionic process similar to that
used in the synthesis of Polymer 19. The principle differences in
this experiment were that the polyisoprene arm MW=2200 (basis NMR
analysis) (1,4-addition=57%; 3,4-addition=43%) and the
DVB/Isoprene=0.195 (wt/wt). Analysis of the coupled polymer by GPC
found about 86% of the polyisoprene chains were coupled to
divinylbenzene cores. The product was isolated (as described for
Polymer 19) as a very viscous mass and reserved for rheology
studies.
It is well known that for linear polymers the viscosity decreases
as the molecular weight of the polymer decreases. We show in the
table below that unexpectedly, this is not true for the star
polymer of the current invention. The viscosities listed in the
table below were measured on a Rheometrics Dynamic Mechanical
Spectrometer at the temperatures noted. It is clear from the table
below that the viscosity of polymers 19 and 20, which have arm
molecular weights of less than 3,000 molecular weight, have
substantially higher viscosities than Polymers 15 and 18 which have
molecular weights greater than 3,000. Therefore there is an optimum
range of molecular weights for star polymers of this type from
about 3,000 to about 7,000. Since epoxidation results in only small
increases in viscosity the same effect of arm molecular weight on
viscosity for epoxidized polymers is expected.
______________________________________ Arm Viscosity Polymer
Molecular Weight (Poise) Temperature (.degree.C.)
______________________________________ 19 1,200 1.5 .times.
10.sup.6 32.8 20 2,200 3,410 26.0 15 3,030 903 26.0 18 4,800 540
25.0 1 6,820 1,074 26.0 ______________________________________
EXAMPLE 15
Preparation of polymers 21, 22, 23, and 24. The following
ingredients were loaded into bottle reactors:
______________________________________ Polymer 21 22 23 24
______________________________________ (grams, except where
indicated) Cyclohexane 231 244 229 249 1,3-butadiene 27.9 28.4 28.5
28.2 Sec-butyl lithium 4.0 ml 4.0 ml 4.0 ml 4.0 ml solution DVB-55
3.97 2.65 0 0 DVB-80 0 0 2.80 1.87 Each of the polymers was
evaluated by GPC. Polybutadiene arm (D) 5300 5200 5200 5600 peak
molecular weight Coupling Efficiency, % 56 59 50 45
______________________________________
Portions of each of the above polymers were dried down after adding
a small amount of a phenolic antioxidant. The samples were analyzed
by .sup.1 H NMR and were measured for complex viscosity by
Rheometrics. NMR results showed that the polybutadiene was 9%
1,2-polybutadiene and 91% 1,4-butadiene, and that less than 2% of
the cyclohexane remained in the polymers. The viscosity results are
shown below.
______________________________________ Residual Measurement
cyclohexane temperature Complex viscosity (%) (.degree.C.) (poise)
______________________________________ Polymer 21 0.8 25 248
Polymer 22 1.2 25 176 Polymer 23 1.3 25 210 Polymer 24 1.9 25 135
______________________________________
Each of the above polymers may be epoxidized as done in Example 2,
Table 1. The star polymers of Example 15 have arms consisting of
butadiene and have slightly lower viscosities than the polymers in
Examples 1-5 because polybutadiene has a lower glass transition
temperature than isoprene. Decreasing the Tg of the polymer
backbone decreases the viscosity near room temperature. Similarly,
increasing the Tg by the inclusion of styrene, high 3,4-isoprene or
high 1,2-butadiene increases the viscosity. For example EKP 202,
made by Shell Chemical Company, is a star polymer similar to those
in the instant invention but containing nearly 50% styrene in the
arms. The molecular weight of the arms is 5,800 and its viscosity
at 24.degree. C. is 732,000 poise, as compared to Polymer 1 which
has a viscosity of 1,074 poise at 26.degree. C. with an arm
molecular weight of 6,820.
EXAMPLE 16
A glass polymerization bottle was equipped with a mechanical
stirrer and a syringe through which chemicals were added. The
bottle was flushed with and maintained under nitrogen. After the
addition of 200 ml of cyclohexane, stirring was initiated. To the
bottle were added 1.0 ml of N,N,N',N'-tetramethylethylenediamine
and 4 drops of diphenylethylene. The solution was titrated with a
s-butyllithium to a light orange color which did not change when an
additional 1.5 ml of 1.4 M s-butyllithium were added. After 3.2 ml
of isoprene (1524 g/arm) were added dropwise, 1.0 ml of
divinylbenzene was added dropwise as the color of the solution
turned to a dark red. The resulting solution was stirred for 20
minutes and 13.0 ml of t-butyl methacrylate (6190 g/arm) was added
dropwise. The solution was stirred for two hours as the color faded
to a light orange. Polymerization was terminated by addition of 10
ml of methanol. The solvent present was removed by evaporation and
the resulting oil was coagulated in isopropyl alcohol, methanol and
water.
EXAMPLE 17
To a glass polymerization bottle flushed with nitrogen and equipped
with a stirrer were added 200 ml of cyclohexane and 20 ml of
tetrahydrofuran and stirring was initiated. After the addition of 4
drops of diphenylethylene as an indicator, the solution was
titrated to an orange color with s-butyllithium. An additional 1.5
ml of s-butyllithium was added. After stirring for 5 minutes, 3.2
ml of isoprene were added and the solution was stirred for 15
minutes as the color turned a light orange. After addition of 1.0
ml of divinylbenzene the solution was stirred for 10 minutes as the
color, initially blood red, turned somewhat lighter. While stirring
continued, 13.0 ml of t-butyl methacrylate were added. The
polymerization was terminated by the addition of methanol and
allowed to stand overnight as the color changed from water white to
light yellow. The solvent was removed by evaporation and the
resulting product was coagulated in methanol and water.
EXAMPLE 18
A glass polymerization bottle equipped with a stirrer was flushed
with nitrogen and 200 ml of cyclohexane and 5.0 ml of diethyl ether
were added. Stirring was initiated and after the addition of 4
drops of diphenylethylene as indicator the solution was titrated
with s-butyllithium to an orange color. An additional 1.5 ml of
s-butyllithium was added and the resulting solution was stirred for
15 minutes. As stirring continued, 3.2 ml of isoprene was added
dropwise. One milliliter of divinylbenzene was then added as the
color of the solution turned blood red. After stirring for 10
minutes as the color of the solution became lighter, 13.0 ml of
t-butyl methacrylate were added as the solution turned light yellow
in color. After 30 minutes the solution was almost water white.
Polymerization was then terminated by addition of methanol and the
polymeric product was coagulated in methanol and water.
* * * * *